Fused aziridines

On heating the fused aziridine (461) at temperatures greater than 250 °C, the resultant product was the furo[3,4-[Pg.155]

The rearrangement of fused triazole (493) produced a fused aziridine and a fused 4-isoxazoline (494) (75T831). 

Likewise, the isomeric fused aziridines 22 and 24, obtained from 1,4,5,6,7,8-hexahydronaph-thalene, undergo bromination. dehydrobromination and ring expansion to the 6,7,8,9-tetra-hydro-3//-3-benzazepine 23 and the 2,7-bridged azepine 25, respectively.61... 

Benzodiazcpine 4-oxides are also produced from 2-(chloromethyl)-l,2-dihydroquin-azoline 3-oxides 11. Thus, the action of potassium /< )7-butoxide on compound 11a gives the fused aziridine 12a, which readily isomerizes to the 5H-], 4-benzodiazepine 4-oxidc 13a on heating. The homolog lib similarly affords the 5//-benzodiazepine oxide 13b on treatment with potassium rerr-butoxide via the aziridine 12b, which, however, could not be isolated. Under different conditions, i.e. with aqueous ethanolic sodium hydroxide, compound 11b is transformed into the tautomeric 3//-1,4-benzodiazepine 4-oxide 14.222... 

In the reaction of fused aziridines with alkene dipolarophiles, the opportunity for stereoselectivity as well as facial selectivity arises since exo- or entfo-isomers can be formed (Scheme 10). In practice, maleic anhydride 6, A-methyl maleimide and JV-phenyl maleimide each reacted exo-stereoselectively with TV-benzyl aziridine 69 to form adducts of type 71 (Scheme 10b), the stereochemistries of which were confirmed by NOE measurement between Hb and He. Similar reaction of the Y-phenyl aziridine 67 with N-Ph maleimide gave a 1 1 mixture of endo-adduct 72 and exo-adduct 73 (Scheme 10c). Adducts 68, 71-73 all exhibited a low-field methano-bridge proton (Ha) in the range 5 3.06-3.60 confirming the syn-facial stereochemistry of the two bridges. 

The pyrrolo[l,2-c]imidazole (223) was produced by addition of DMAD to an azomethine ylid resulting from photochemical ring opening of a fused aziridine,299 and the adduct 224 resulted from... 

Fused aziridines are interesting compounds owing to the fact that the strained three-membered ring can easily open and cause dipolar cycloaddition reactions as well as their photochromic properties. Therefore, most of this chapter covers the chemical and photochemical properties of bi- and tricyclic aziridines. Some properties of aziridinyl ketones are also reviewed, in particular, reactions leading to aziridinyl anils. 

Thus, acid-catalyzed transformations of fused aziridines include cleavage of the C-N bond of the aziridine cycle. A reaction has also been described where the C-N bond of the imidazole cycle is broken [88]. It was shown that a rearrangement leading to pyrimidine 111 takes place under the action of sodium methylate with azirenoimidazoles 110 (Scheme 1.31). 

Most of the chemical properties of fused aziridines described in the literature are concerned with cycloaddition reactions. For example, it was shown in one of the first works [93] that refluxing azirenoimidazole 72 with different compounds containing multiple C-C bonds in / interaction with diethyl acetylene dicarboxylate 116, diethyl fumarate 118 or 1,4-diarylbut-2-ene-l,4-diones 120 gives rise to the cycloadducts 117,119 and 121, respectively... 

Regiospecific 1,3-dipolar cycloaddition reactions of dihydropyridines and some organic azides lead to high yields of fused aziridines—2,7-diazabicy-cli[4.1.0]hept-3-enes 337 [365, 366, 367] (Scheme 3.112). The reaction proceeds via the preliminary formation of an intermediate 336 and the elimination of nitrogen. Reaction of pyrimidine 334 with less reactive methoxycarbonyl and benzoyl azides does not occur [367]. Compounds 337 exhibit significant analgesic, antibacterial and antifungal activities [367]. 

The nitrogen atom of the pyrrolidine moiety in a dihydrobenzothiazole internally displaced the bromine on the carbocyclic ring, forming a pyrrolobenzothiazole with a fused aziridine ring <83CPB1518>. 

Thermolysis of 2-azido cinnamates containing oriho-vinyl, -styryl, -allyl, and cycloalkenyl substituents led generally to mixtures of products, including isoquinolines, azepines, indoles, fused aziridines and cyclopropanes, arising from the decomposition of the intermediate dihydrotri-azole cycloadducts or azirines89. 

When an aziridine ring is fused at the 2,3-bond to another ring system, the only ring opening structurally allowed is a disrotatory rotation, which must be photolytically performed as discussed above. Thus, the fused aziridine 8 on irradiation generates syn-azomethine ylide 9, which is captured by an acetylene to give a bicyclic cycloadduct (68CPB764). 

Other types of ring-fused aziridines, fused at the 1,2-bond, similarly generate azomethine ylides whose skeleton is partially incorporated in a ring system (68JOC1097 69JOC171 86JCS(P1)1119). 

Azomethine ylides 221 of the ester-stabilized type can be generated by ring opening of the corresponding ring-fused aziridines and can cycloadd to 2-aryl-1-azirines in a stereoselective manner to give 222 (86JCS(P1)1119). 

An internal addition of nitrenes is also possible, when the double bond is located at a suitable distance. The highly strained fused aziridines formed undergo immediate hydrolysis to hydroxymethyl pyrrolidines. With acyl azides yields were low, as the respective isocyanates were the major products. Examples are the conversions... 

A systematic study of the behavior of simple monocyclic and fused aziridines towards electron impact shows strong parent mass peaks (usually more than 10% of the base peak intensity) and... 

A ring-fused aziridine (48), in which the Ar and ester groups are cis, undergoes a stereospecific conrotatory ring opening leading to ( ),(Z)-azomethine ylide (49), which is trapped with an aziridine... 

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